Transmission Electron Microscopy Grids Research Articles

Layer-Dependent Hydrazine Adsorption Properties in Few-Layer WS2

We have developed a lithography free technique for the fabrication of two-dimensional material based devices for electrical characterization. We fabricated few-layer and multilayer WS2 devices using a transmission electron microscope (TEM) grid as a shadow mask, and its transport characteristics were studied by electrical measurements. WS2 samples were synthesized by first depositing WO3 followed by sulfurization and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. Each sample was exposed to hydrazine at varying pressures, and their electrical resistances were monitored during adsorption (exposing to hydrazine vapor) and subsequent desorption (by pumping). The WS2 sample consisting of two layers showed a decrease of resistance upon exposure to hydrazine vapor and showed complete reversibility upon pumping. The WS2 sample with three layers showed a decrease of resistance during exposure but showed only partial recovery during desorption. In contrast, the multilayered (12 layers) WS2 sample showed an initial decrease followed by a continued increase of the resistance upon exposure to hydrazine with little or no reversibility upon pumping. The charge transfer from N2H4 to WS2 is believed to be responsible for the decrease of the resistance. Trapping of N2H4 molecules within the multilayers of WS2 causing charge redistribution and possible chemical reactions may be responsible for the increase in resistance during the adsorption and complete irreversibility of resistance during desorption. The experimental results are explained with the help of computational calculations performed by employing the density functional theory (DFT) framework, as implemented in the Vienna Ab-initio Simulation Package (VASP).

Graphene-WS2 heterostructures by a lithography free method: their electrical properties

We have developed a lithography free technique for the fabrication of two-dimensional (2D) material based heterostructures. We fabricated graphene-WS2 heterostructured devices using a transmission electron microscope grid as a shadow mask and their electrical transport characteristics were studied by electrical and magneto transport measurements. Graphene was directly deposited on a Si/SiO2 substrate by radio frequency plasma enhanced chemical vapor deposition. WS2 was synthesized by first depositing WO3 followed by sulfurization. The temperature dependence of the resistance and magnetoresistance are measured for graphene, WS2, and graphene-WS2 heterostructure. At low temperatures, the transport is found to follow the variable-range hopping (VRH) process, where logarithmic R exhibits a T−1/3 temperature dependence, an evidence for the 2D Mott VRH transport. The measured low-field magnetoresistance also exhibits a quadratic magnetic field dependence ∼B2, consistent with the 2D Mott VRH transport.

Advances in Graphene‐Based Liquid Cell Electron Microscopy: Working Principles, Opportunities, and Challenges

AbstractImaging materials and biological structures in a liquid environment pose a significant challenge for conventional transmission electron microscopy (TEM) due to stringent requirement of ultrahigh vacuum design in the microscope column. The most recent liquid‐cell TEM technique, graphene liquid‐cell (GLC) microscopy, employs only layers of graphene to encapsulate liquid specimens. Recent efforts with GLC–TEM have demonstrated superior imaging resolution of beam‐sensitive specimens. Herein, the parameters that affect the quality of GLC analysis, including the graphene transfer onto TEM grids, are reviewed. Several important factors that affect the in situ TEM imaging of specimens, including the variations in GLC geometries and capillary pressure are discussed. The interaction between the electron beam and the liquid along with the possibility for artifacts or the formation of radical ions is also highlighted in this review. The scientific discoveries enabled by GLC–TEM in the areas of nucleation and growth of crystals, corrosion, battery science, as well as high‐resolution imaging of organelles and proteins are also briefly discussed. Finally, possible future research directions of GLC–TEM and the associated challenges are discussed. The synergistic effort to accomplish the proposed research directions has the potential to yield new discoveries in both materials and life sciences.

A Computer-Vision-Guided Robot Arm for Automatically Placing Grids in Pioloform Film Preparation

Preparing pioloform/formvar support films on transmission electron microscopy (TEM) grids is a routine laboratory procedure in practically all electron microscopy units. In current practice, these grids are manually placed on the support film one by one using special tweezers, a process requiring a steady hand. The work is often ergonomically awkward to continue for a longer period of time. In this article, we describe a low-cost, computer vision-guided robot arm that automatically places the grids on the film. The success rate of the prototype robot is 90%, which is comparable to an experienced laboratory technician.

Hierarchically Patterned Elastomeric and Thermoplastic Polymer Films through Nanoimprinting and Ultraviolet Light Exposure.

The surface relief structure of polymer films over large areas can be controlled by combining nanoscale imprinting and microscale ultraviolet–ozone (UVO) radiation, resulting in hierarchical structured surfaces. First, nanoscale patterns were formed by nanoimprinting elastomer [poly(dimethylsiloxane) (PDMS)] films with a pattern on a digital video disk. Micron-scale patterns were then superimposed on the nanoimprinted PDMS films by exposing them to ultraviolet radiation in oxygen (UVO) through a transmission electron microscopy grid mask having variable microscale patterning. UVO exposure leads to conversion and densification of PDMS to SiOx, leading to micron height relief features that follow a linear scaling relation with pattern dimension. Further, the pattern scopes are shown to collapse into a master curve by normalized feature values. Interestingly, these relief structures preserve the nanoscale features. In this paper, the influence of the self-limiting PDMS densification, wall stress at the boundary of micro-depression, and UVO exposure energy is studied in control of the micro-depression scale. This simple two-step imprinting process involving both nanoimprinting and UV radiation allows for facile fabrication of the dimension adjustable micro–nano hierarchically structures not only on elastomer films but also on thermoplastic polymer films. Coarse-grained molecular dynamics simulations were performed to correlate the surface tension and elastic properties of polymeric materials to the deformation of the pattern structure.

Magnetic Field-Induced Assembly of Superparamagnetic Cobalt Nanoparticles on Substrates and at Liquid-Air Interface.

Superparamagnetic cobalt nanoparticles (Co NPs) are an interesting material for self-assembly processes because of their magnetic properties. We investigated the magnetic field-induced assembly of superparamagnetic cobalt nanoparticles and compared three different approaches, namely, the assembly on solid substrates, at water-air, and ethylene glycol-air interfaces. Oleic acid- and trioctylphosphine oxide-coated Co NPs were synthesized via a thermolysis of cobalt carbonyl and dispersed into either hexane or toluene. The Co NP dispersion was dropped onto different substrates (e.g., transmission electron microscopy (TEM) grid, silicon wafer) and onto liquid surfaces. Transmission electron microscopy (TEM), scanning force microscopy, optical microscopy, as well as scanning electron microscopy showed that superparamagnetic Co NPs assembled into one-dimensional chains in an external magnetic field. By varying the concentration of the Co NP dispersion (1-5 mg/mL) and the strength of the magnetic field (4-54 mT), the morphology of the chains changed. Short, thin, and flexible chain structures were obtained at low NP concentration and low strength of magnetic field, whereas they became long, thick and straight when the NP concentration and the magnetic field strength increased. In comparison, the assembly of Co NPs from hexane dispersion at ethylene glycol-air interface showed the most regular and homogeneous alignment, since a more efficient spreading could be achieved on ethylene glycol than on water and solid substrates.

The evolution of soot morphology and nanostructure along axial direction in diesel spray jet flames

This study aims at providing new insights into the soot formation and oxidation processes in diesel spray jet flames under the diesel-like conditions. Soot particles are sampled within a reacting diesel jet spray flame in a constant-volume combustion chamber under diesel-like high-temperature and pressure ambient conditions. The experiments are conducted with an injector hole of 0.28 mm and injection mass of 30 mg per shot. Soot particles at different locations along the axis of the diesel jet flame are sampled by a thermophoretic probe, and the variation of soot morphology and nanostructure of the sampled soot particles along the axial location in the flame is analyzed by using the transmission electron microscopy (TEM). At upstream of the jet flame, large “liquid-like” particles are observed in the TEM images. As these particles are delivered to the downstream, (1) there are many immature primary particles formed on the surface of large “liquid-like” particles, and (2) they are carbonized into the larger soot aggregates with the matured structure, and then at last, (3) the larger soot aggregates gradually break up into the smaller particles with relatively compact structure. Both the diameter of primary particles and radius of gyration of the soot aggregates decrease as the distance between the injector nozzle tip and the center of TEM grid is increased, while the opposite trend is found in the behavior of the fractal dimensions of soot aggregates. The high resolution TEM images show that the soot primary particles exhibit the turbostratic state at the upstream of the jet flame, while more matured structures with the graphitic crystallite in outer shell and several fine particles in the inner core are observed as the sampling distance from orifice is increased. The average fringe length increases while the average tortuosity and separation decrease with the distance from the nozzle. These results suggest that the mechanism of mature soot aggregates generated directly from the large “liquid-like” particles should be one of the ways of soot particle formation along the axis of diesel jet flames.

Effects of radio frequency power and gas ratio on barrier properties of SiOxNy films deposited by inductively coupled plasma chemical vapor deposition

SiOxNy barrier films were deposited at low temperature of ~ 23 °C using inductively coupled plasma chemical vapor deposition (ICP-CVD). When radio frequency power increased at constant ratios of Ar/SiH4 and O2/(O2 + N2), respectively, of 4.5 and 0.1, the aggregation tendency of nanoparticles slightly decreased, whereas when the ratio of Ar/SiH4 was changed from 4.5 to 41, almost spherical nanoparticles, each of which was isolated without aggregation, were observed. Such a near spherical nanoparticle without aggregation produced highly dense films with enhanced barrier property. However, heavily aggregated nanoparticles produced very porous films with deteriorated barrier property. In other words, the film density and barrier property depended significantly on whether nanoparticles were isolated or aggregated. To investigate the formation mechanism of dense SiOxNy barrier film, a transmission electron microscope grid membrane was exposed for 5 s to capture nanoparticles generated in the gas phase using a shutter above the grid membrane during ICP-CVD and the grid membrane was observed by scanning transmission electron microscope. The formation mechanism of the barrier film could be best explained by non-classical crystallization of CVD films, where nanoparticles formed in the gas phase contribute to the film formation.

Determining fractal properties of soot aggregates and primary particle size distribution in counterflow flames up to 10 atm

Abstract Experimental investigations of soot morphology are performed in counterflow flames of N2-diluted ethylene and air, up to 10 atm. A thermophoretic sampling device is attached to a pressure vessel containing a counterflow burner where flames with an ethylene mole fraction of 0.3 are stabilized at 3, 5, and 6 atm. To allow measurements at higher pressures, the fuel mole fraction is lowered to 0.2 to reduce the soot loading and flames are studied at 5, 7, and 10 atm. Thermophoretic sampling of the soot zone is performed using TEM grids. The sampling process causes minimal flame disturbances. Soot collected on TEM grids is analyzed under transmission electron microscope (TEM). Primary particle size distributions are inferred at each pressure by manually analyzing the primary particles from TEM images. Fractal properties of soot at each pressure are also obtained by analyzing the TEM images at comparatively low magnifications. Mean primary particle diameter increases from 17.5 to 47.1 nm as the pressure is increased from 3 to 10 atm, whereas the fractal dimension and prefactor do not change with pressure up to 10 atm. For the flames studied here, fractal dimension lies between 1.61 and 1.67 whereas fractal prefactor varies between 1.68 and 1.86 without following any apparent trend with pressure.

A quasi in situ TEM grid reactor for decoupling catalytic gas phase reactions and analysis

We present a versatile grid reactor setup for transmission electron microscopy (TEM), which is able to track catalytic conversion on TEM amounts of sample. It is based on the concept of decoupling catalytic gas-phase reactions from the structural analysis of identical particles before and after reaction. The system has superior properties in terms of image resolution and long-term measurements compared to conventional in situ TEM analysis. Monitoring catalytic conversions on a TEM grid is enabled by proton-transfer reaction mass spectrometry. In addition, identical location imaging benefits from a secure transfer of the sample between TEM and the reactor system by vacuum transfer holders. Using Pt and Cu/ZnO/Al2O3 as an example we show that structural changes of identical particles or areas of a Pt foil before and after reactive experiments can be tracked. During catalytic testing the samples are exposed to homogeneous reaction conditions. The concept minimizes electron-sample and electron-atmosphere interactions and can prospectively be considered as complementary tool to in situ TEM analysis.

Effect of Bias Applied to the Substrate on the Low Temperature Growth of Silicon Epitaxial Films during RF-PECVD

The deposition behavior of silicon films by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) was studied by nonclassical crystallization, where the building block of deposition is charged nanoparticles generated in the gas phase of the reactor. To confirm the existence of nanoparticles in the RF-CVD reactor, nanoparticles were captured on the membrane of the transmission electron microscope (TEM) grid under the condition of the DC bias applied to the holder. The capturing behavior of nanoparticles depended on the bias and the conductivity of the membrane. Also, to examine the effect of the bias on the epitaxial growth, films were deposited on the silicon wafer substrate under the condition of the biases of 0, +1000, and −1000 V applied to the substrate holder. A fully epitaxial film could be grown on a silicon wafer at 550 °C under the bias of −1000 V.

The Morphology and Assembly of Respiratory Syncytial Virus Revealed by Cryo-Electron Tomography

Human respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in young children. With repeat infections throughout life, it can also cause substantial disease in the elderly and in adults with compromised cardiac, pulmonary and immune systems. RSV is a pleomorphic enveloped RNA virus in the Pneumoviridae family. Recently, the three-dimensional (3D) structure of purified RSV particles has been elucidated, revealing three distinct morphological categories: spherical, asymmetric, and filamentous. However, the native 3D structure of RSV particles associated with or released from infected cells has yet to be investigated. In this study, we have established an optimized system for studying RSV structure by imaging RSV-infected cells on transmission electron microscopy (TEM) grids by cryo-electron tomography (cryo-ET). Our results demonstrate that RSV is filamentous across several virus strains and cell lines by cryo-ET, cryo-immuno EM, and thin section TEM techniques. The viral filament length varies from 0.5 to 12 μm and the average filament diameter is approximately 130 nm. Taking advantage of the whole cell tomography technique, we have resolved various stages of RSV assembly. Collectively, our results can facilitate the understanding of viral morphogenesis in RSV and other pleomorphic enveloped viruses.

Formation and evolution of tar balls from northwestern US wildfires

Abstract. Biomass burning is a major source of light-absorbing black and brown carbonaceous particles. Tar balls (TBs) are a type of brown carbonaceous particle apparently unique to biomass burning. Here we describe the first atmospheric observations of the formation and evolution of TBs from forest fires. Aerosol particles were collected on transmission electron microscopy (TEM) grids during aircraft transects at various downwind distances from the Colockum Tarps wildland fire. TB mass fractions, derived from TEM and in situ measurements, increased from <1 % near the fire to 31–45 % downwind, with little change in TB diameter. Given the observed evolution of TBs, it is recommended that these particles be labeled as processed primary particles, thereby distinguishing TB formation–evolution from secondary organic aerosols. Single-scattering albedo determined from scattering and absorption measurements increased slightly with downwind distance. Similar TEM and single-scattering albedo results were observed sampling multiple wildfires. Mie calculations are consistent with weak light absorbance by TBs (i.e., m similar to the literature values 1.56−0.02i or 1.80−0.007i) but not consistent with absorption 1 order of magnitude stronger observed in different settings. The field-derived TB mass fractions reported here indicate that this particle type should be accounted for in biomass burning emission inventories.

A sampler designed for nanoparticles and respirable particles with direct analysis feature

A sampler has been designed to collect particles in the nanometer and respirable sizes directly onto a membrane filter and transmission electron microscopy (TEM) grid. The novel design aspects of this sampler include the selection of the diameter of the inlet probe, geometry of the sampler, and the resulting air flow to the sampler. Together, they control the cutoff diameter, which was determined experimentally to be a mass median aerodynamic diameter (MMAD) of 3.8 μm. The maximum aerodynamic diameter entering the sampler is designed to be approximately 8 μm. Nanometer-sized particles are collected on both the filter and grid through diffusion, as confirmed by testing with aluminum oxide engineered nanoparticles collected on the filter which measured a count median diameter (CMD) of 500 nm and a geometric standard deviation (GSD) of 1.97. The primary particles and small agglomerates collected on the grid have a CMD of 100 nm and GSD of 2.3. This diffusion sampler collected close to, if not 100%, of the particles entering the sampler. The sampler is easily wearable for personal exposure and environmental sampling, operates at 0.3 L/min, and can collect particles in various settings at indoor and outdoor environments. Particles are analyzed directly by transmission electron microscope on the grid and by scanning electron microscope on the filter to assess the exposure through particle counts and elemental composition analysis.

Novel Applications of Focused Ion Beam Technique for Planetary Sample Analyses

We are using innovative FIB techniques to prepare samples of planetary materials for different types of coordinated analyses using ion microprobes, synchrotron beamlines, and specialized transmission electron microscopy (TEM) techniques. In these cases, the FIB sample preparation is the critical step in enabling these specialized analyses. We discuss several examples below utilizing the FEI Quanta3D instrument at the NASA Johnson Space Center. Trace element analyses utilizing synchrotron x-ray fluorescence. The trace element content of mineral grains in comet dust provides important clues on their formation and processing in the early solar system. We preformed coordinated analyses of a comet dust particle that had been prepared using ultramicrotomy for TEM analysis. Following the TEM analyses, we extracted a 70 nm thick section from a region of the carbon (C) film of the TEM grid, for additional analyses. A carbon ring ~2-3 μm thick was deposited on top of the C film using the FIB. The C film on the outer rim of the ring was milled away using various patterns to uniformly release the stresses on the film, preventing rupture and collapse, and was attached to the micromanipulator needle. We then isolated the ring completely and transferred the section to a silicon sample holder for analysis using the HXN (hard X-ray nanoprobe) beamline at NSLSII at Brookhaven National Lab. Coordinated Analyses of Presolar Grains. Rare sub-m presolar grains that originate in evolved stars and supernovae, occur in primitive astromaterials and are identified by their exotic isotopic compositions. Coordinated analyses of these grains using NanoSIMS, TEM, and other techniques on the same grain is enabled by innovative FIB sample preparation. In order to obtain subsequent isotopic analyses of Mg and Fe, contributions from surrounding grains were minimized. We precisely deposited a protective cap of Pt on top of the grain to preserve the grain of interest and then milled away about 5 μm diameter of the surrounding material. Following the isotopic analyses, the spindle was extracted and thinned to electron transparency for TEM microstructural analyses. In situ heating TEM experiments on lunar samples. We extracted a FIB thin section from Apollo 17 lunar rock 76015. To avoid ion-beam damage, e-beam deposition was used to deposit the first 500 nm of the C strap, followed by ion beam-assisted deposition of ~3 μm carbon. We performed an ex situ lift-out of the section and placed the section on one of the elements of a microelectromechanical systems (MEMS) - specialized heating substrate and attached the section to the substrate by depositing small C straps with the FIB. The heating chips utilize silicon nitride windows to support the samples and provide uniform heating while enabling TEM imaging. The heating chip was loaded into a Hitachi “Blaze” heating holder and analyzed using a Hitachi HF5000 at the University of Arizona.

Nanostructure characterization of soot particles from biodiesel and diesel spray flame in a constant volume combustion chamber

This study investigates the effect of biodiesel fuels on morphological characteristics of soot particles from spray flame in a constant volume combustion chamber. The experiments were carried out under simulated diesel engine condition. The auto-ignition of injected fuel was carried out at an ambient pressure of 5 MPa and ambient temperature of 978.15 K. The soot particles were captured with a transmission electron microscope (TEM) grid inside the flame by thermophoretic effect. They were characterized as primary particle diameter, graphene layer (fringe) length, fringe tortuosity, and fringe spacing based on the image processing from original TEM image. Three different kinds of biodiesel fuels, waste cooking oil biodiesel, Jatropha biodiesel and Karanja biodiesel were used in the test. Conventional diesel fuel was utilized as a baseline fuel for the comparison. The tested fuels were injected with injection pressures of 40, 80, and 120 MPa by means of common-rail injection system. The experimental result showed that all of the biodiesel fuels had smaller primary particle diameter than that of conventional diesel regardless of injection pressures. The soot particles from biodiesel fuels were also distinguished showing characteristically shorter fringe length and lower tortuosity. These experiments unveiled a correlation between the nano-structural parameters for the early stage of oxidation inside the flame.

Transmission Electron Microscopic Observation of Both Ionomer and Pt Distribution and Their Effects on Cathode Performance for Polymer Electrolyte Fuel Cells

In the electrode of a polymer electrolyte fuel cell (PEFC), the distribution of perfluorosulfonic ionomer on the Pt catalyst supported on carbon black (CB) significantly affects the fuel cell performance. The observation of the distribution of the ionomer and Pt catalyst on the carbon support are important for the improvement of PEFC performance. Recently, the direct observation of the ionomer with transmission electron microscopy (TEM) without damage by the electron beam has become possible due to technological improvements.In this study, four types of cathode catalyst inks were prepared in which the added amount of the perfluorosulfonic ionomer, prepared by AGC, was varied with respect to the CB (I/C ratio; I, weight of fluoro-ionomer; C, weight of graphitized CB (GCB)). The membrane electrode assemblies (MEAs) were made from catalyst layers (CLs), which were decals printed with these inks by the hot-press method. The catalyst powders collected from the cathodes were placed on a TEM grid without pretreatment. The ionomer distribution on GCB-supported Pt catalysts was observed with a high resolution TEM (Hitachi HT7700) with a low acceleration voltage (80 kV).1 The pore distribution of each sample was measured by use of N2 absorption analysis. The current-voltage (I-V) performances of the MEAs were also evaluated, and the effects of the ionomer distribution on the cell performance were investigated. A TEM image of the catalyst collected from the cathode (I/C = 0.8) is shown in Fig. 1a. The amorphous structure of the ionomer is able to be clearly observed on the surfaces of both the GCB and the Pt nanoparticles with the low acceleration voltage, high resolution TEM. A TEM image of the electrode catalyst of I/C = 1.6 sample is shown in Fig. 1b. The amorphous areas increased with increasing ionomer content and were observed more frequently. Agglomerations of Pt particles were also observed in some areas. In a previous study, Pt agglomeration and re-deposition due to sulfonate groups included in the high IEC ionomer were reported.2 These results suggested that the increased acid concentration of the ionomer around the Pt nanoparticles can cause severe Pt agglomeration. The mobilities of both ionomer and Pt particles might be influenced by the surface of the CB, and those on GCB would be expected to be larger than those on CB due to the smooth surface of graphite. The I-V performance of the MEAs is shown in Fig. 2. The performance increased with increasing I/C from 0.4 to 0.8 and 1.2 and then decreased for 1.6. Improvements in current density were considered to be due to increases in the number of proton-conductive pathways due to the ionomer in the CLs. The pore distribution of various the I/C samples were measured by use of N2 absorption analysis. The pore volumes of both nanopores of 2-5 nm and primary pores of 5-10 nm for the I/C = 1.6 cathode were decreased. The performance decrease for I/C = 1.6 is considered to be due to a decrease in the number of oxygen transport paths due to occupation of the pores of the carbon support with the ionomer. References (1) Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources, 315, 179 (2016). (2) R. Shimizu, Y.-C. Park, K. Kakinuma, A. Iiyama, M. Uchida, J. Electrochem. Soc., 165 (6) F3063-F3071 (2018) Figure 1

Mobility and Poisoning of Mass-Selected Platinum Nanoclusters during the Oxygen Reduction Reaction

A major challenge in electrocatalysis is to understand the effect of electrochemical processes on the physicochemical properties of nanoparticle or nanocluster (NC) ensembles, especially for complex processes, such as the oxygen reduction reaction (ORR) considered herein. We describe an approach whereby electrocatalysis at a small number of well-defined mass-selected Pt NCs (Pt923±37, diameter, d ≈ 3 nm), deposited from a cluster beam source on carbon-coated transmission electron microscopy (TEM) grids, can be measured by a scanning electrochemical cell microscopy (SECCM) setup, in tandem with a range of complementary microscopy and spectroscopy techniques. The SECCM setup delivers high mass transport rates and allows the effects of transient reactive intermediates to be elucidated for different Pt surface coverages (NC spacing). A major observation is that the ORR activity decreases during successive electrochemical (voltammetric) measurements. This is shown to be due to poisoning of the Pt NCs by carbon...

Using Graphene Liquid Cell Transmission Electron Microscopy to Study <em>in Situ</em> Nanocrystal Etching

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching.

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.